A researcher would like to examine how the chemical tryptophan, contained in foods such as turkey, can affect mental alertness. A sample of n = 9 college students is obtained and each student’s performance on a familiar video game is measured before and after eating a traditional Thanksgiving dinner including roast turkey. The average score dropped by M = 14 points after the meal with SS = 1152 for the difference scores.

a. Is there is significant difference in performance before eating versus after eating? Use a two-tailed test with α = .05.

b. Compute r2 to measure the size of the effect.

c. Write a sentence demonstrating how the outcome of the test and the measure of effect size would appear in a research report.